This invention relates to the treatment of leafy agricultural products, and more particularly concerns the treatment of tobacco and silage corn to minimize the content of nitrate originating from fertilizers.
Corn which is intended as cattle feed is generally comminuted and stored in silos until ready for use. Such silage material may owever contain large amounts of nitrate, particularly when the corn crop had been fertilized with nitrate-containing fertilizer and then experienced dry growth conditions. The high nitrate content of the silage may be fatal to cattle.
Tobacco leaf and stem materials generally contain quantities of potassium nitrate ranging between 2% and 10% by weight of the tobacco material. Amongst the several types of tobacco utilized for the manufacture of cigarettes, burley varieties are generally found to have the highest nitrate content. Stem materials, which may be incorporated in various physical forms into the total combustible mixture or "filler" held by the paper wrapper, often contain higher nitrate contents than the corresponding leaf or lamina portions.
During the combustion process, the nitrate content of the tobacco produces nitric oxide as a component of the gaseous phase of the smoke stream. If the smoke is collected and held a period of time for analytical purposes, the initially formed NO produces NO.sub.2, N.sub.2 O.sub.3 and N.sub.2 O.sub.4, generally referred to as "nitrogen oxides".
It has long been sought to minimize the nitrogen oxide content of cigarette smoke. Removal of the precursor potassium nitrate has been achieved by various techniques applied by way of water-based treatment of tobacco, for example, aqueous extracts of tobacco may be subjected to concentration and/or cooling treatments which cause formation of potassium nitrate crystals separable from the remaining extract liquor by filtration. Aqueous tobacco extracts have also been subjected to ion-exchange and microbial treatments for the removal of dissolved nitrate ions.
The extraction of selected water soluble components from tobacco is relatively expensive, and may cause considerable alteration of smoking quality. Such extractions are in fact generally conducted in operations wherein stem materials and recovered fines are pulped and converted to a sheet structure which is subsequently blended into tobacco leaf filler material.
The reaction of hydrochloric acid with the inorganic nitrate ion as in potassium nitrate is well known, and may be expressed by the following equation. EQU 4HCl+KNO.sub.3 .fwdarw.KCl+NOCl+Cl.sub.2 +2H.sub.2 O
When tobacco or silage crop is treated with hydrochloric acid, the above-noted reaction causes removal of nitrate ion with attendant formation of the volatile species NOCl, Cl.sub.2 and H.sub.2 O. However, the NOCl and Cl.sub.2 are so highly reactive that they interact with tobaco or silage crop constituents to form undesirable non-volatile chlorinated organic species.
It is accordingly an object of the present invention to provide a relatively inexpensive process for the removal of inorganic nitrate from leafy agricultural materials.
It is another object of this invention to provide a process as in the foregoing object which does not involve a water-extraction of the agricultural material.
It is a further object of the present invention to provide a process of the aforesaid nature which utilizes HCl without producing significant amounts of chlorinated organic compounds within the treated material.
These objects and other objects and advantages of the invention will be apparent from the following description.